Unusual role of positive Indian Ocean Dipole in the record-low tropical cyclone genesis over the Western North Pacific in 2023

Abstract

The number of tropical cyclones (TCs) over the western North Pacific (WNP) dropped to a record low in 2023, with less than 40% forming during the boreal autumn. While a strong El Niño, positive Indian Ocean Dipole (pIOD), and strong tropical North Atlantic warming coexisted, their relative contributions to the suppressed TC genesis remain unclear. Through observational analyses and model experiments, we demonstrate that the tropical Atlantic and Pacific exerted minimal influence on TC genesis over the WNP. In contrast, the pIOD played a dominant role in suppressing TC activities over the central WNP, where the decline was most pronounced. Specifically, the pIOD induced easterly wind anomalies over the Indo-western Pacific, leading to descending anomalies over the WNP that inhibited TC genesis. Our findings highlight the importance of incorporating the IOD into future seasonal TC forecasts to improve its prediction skill.